for Engineers wanting to pursue PhD

There are number of queries of Engineers {Who probably got strayed into tech biz but had a inner longing to do Physics!:) } who would like to pursue a research Career, so this blog.

You are most welcome to do a PhD in Astronomy and Astrophysics. Visit IIA website for details of application procedure, exams and interviews to be taken. PhD in Computation or Instrumentation or Electronics based experimentation, Observational Astronomy would be possible.

Not much prior knowledge of Astronomy is expected as you will be given good grinding in Research Training Program (RTP) in the first year of joining. {You need to clear it well to get into second year!}

Many institutes have their own entrance tests and interviews. Check their websites and call their offices.

You can prepare for JEST and/or NET Physics and/or GATE Physics as follows:-

0.Check their syllabus

1. Brush up your FE Fundamentals of Physics book

2. Refer

*Fundamentals of Physics by Resnik and Halliday.

*Concepts of Modern Physics by Arthur Beiser.

*Electrodynamics by Griffith

3. Catch up with some sample papers from the same agency where you apply for these exams

4. Solve loads of problems. You Cant Survive In Research if you don't like to solve problems. Only understanding Stuff is not enough... :) ''Physics by Example'' by Rees is a good start. Actually, any good problem solving book with detailed solutions is good enough. Check solution after you have attempted the problem, and see where you made mistake, if any.

This is not necessarily the most complete and sufficient prep! Apply for a YES!+ also... check www.yesplus.org

All the best!

The younger Twin

Thanks to Amrita for asking this question about Twin Paradox. It was a thoughtful question, and the right questions at right time can lead to Big progress and good understanding. I have quoted below this dialog as it is. It reminds me of one story from Puranas, which indicates that the superfast(close to c) time travel could have been possible earlier.

The story goes like this:-

There was a King and he had a pretty daughter. He couldn't find a suitable groom for his pretty daughter, and so he set himself and her on a travel to Brahmaloka. When he reached Brahmaloka, Brahma gave him blessing and asked him to marry her to the King of a certain country on Earth. Happy, the King traveled back to the Earth with his daughter. Coming to the earth, he was so surprised that his city, his buildings and people were not there at all. In his City, he himself and all the human beings were as tall as a coconut tree. And he was shocked to see the human beings in the size of 5-6 feet, so small compared to him and her daughter. Upon inquiry, the King got to know that their civilization used to exist several thousand centuries ago! Though the King and his daughter had only aged by an year or so, the time had elapsed much faster on the earth. The King got his daughter married to a noble Prince and they lived happily ever after.

Conclusion:- the King and his daughter had traveled very fast, and Brahma loka could have been a really far away place!

Thanks

Amrita said...

Hi,I was reading theory of relativity and found that "Time Dilation is a reciprocal effect",if it is so then why in case of twin paradox,one of the twins who goes to the space and come back, remains younger than the other who stays back on the earth!

November 23, 2009 10:41 PM

Abhay Karnataki said...

good question.
now here we have to understand that though there is no single absolute inertial frame for all observers, you can definitely make out if your frame is inertial or not.
if you are in a car and close your eyes, then even when the car turns, your body bends to one side or other, showing the acceleration, and hence non-inertial nature of the frame attached to the car.
Similarly, in the twin brothers travel, one brother is definitely getting accelerated at the end of the journey, and he is the one who comes out to be younger. the brother in his rest frame doesn't experience any acceleration at any time.
if the other brother would not have returned any time, then the time dilation is exactly reciprocal.

November 23, 2009 10:47 PM

Newton's laws of motion

The Newton's first law of motion states ''A body continues to be in the state of rest or constant motion unless it is acted upon by an external agency.''

The Newton's second law states "The acceleration of a particle is directly proportional to the external force applied on it and inversely proportional to the mass of the particle."

The Question that should naturally arise in a student's mind is, if F=0, what is the need to state the first law separately, because it can be deduced from second law that a=0 and hence velocity is constant. So is the first law necessary!?

Ans:-

The measurement of distances and time are done in a reference frame. The first law of motion defines a reference frame where the motion doesn't change unless and otherwise acted upon by an external agency. e.g. you could be in a car that's going along a hillside region of ups and downs and turns. In a reference frame attached to the car, a particle within the car will not remain stationary or in constant motion. So in such a reference frame, the first law is not applicable, and such frame is ruled out in the Newton's scheme of study of dynamics directly. But you could choose a frame fixed to earth say, in which the first law will hold, even if Car moves around. Such a frame where first law holds, is called inertial frame of reference- inertia of a body is maintained. Now again, a frame attached to earth is not infinitely inertial frame of reference, as the earth itself rotates and revolves. for a trajectory of a plane e.g., Earth's frame becomes non-inertial. So you can use a bigger frame at rest w.r.t Sun. But then even it is non-inertial, when you discuss motion of comets, as the Sun moves in the galaxy... So use even bigger frame at the center of galaxy... and finally even bigger in the outer space in between galaxies and galaxy clusters, so that first law is valid in that reference frame.

Either you can keep changing a reference standard for inertial frame, or you can say that so and so part of the space is a good ''local'' inertial reference frame, observed for a so and so interval of time, over which the first law is valid.

In such an inertial frame, second law can be used to calculate the acceleration 'a'.

Lectures on General Theory of Relativity

Lectures on General Theory of Relativity, by Prof. T. Padmanabhan have been uploaded here.

T. Padmanabhan is a renowned Physicist who has written excellent books on Theoretical Astrophysics.

Heartbeat of the Sun

One of the greatest opportunities in a research Institute is to get to listen to great Scientists. Here is the news article describing how a team of scientists studying Sun is extracting the information of the internal activities of the Sun. 

The studies of Sun using Visible or any other electromagnetic radiation is limited to the photosphere. Only Neutrinos produced in the nuclear reactions at the core of the Sun carry information about the layers inside Sun, to us. In what amounts to finding needle in the hey, the scientists have discovered a subtle ripple in the overall movement of the solar surface. The technique is to get the Fourier transform of the Fourier transform, thus giving an indication to the patterns in the frequency spectrum! It is like finding the octaves in the music of piano, and detecting the presence of piano in a grand symphony. The waves originate at the core of Sun because of gravitational disturbances. Rafael A. Garcia, DSM/DAPNIA/Service  d'Astrophysique, France explained this in a colloquium at our Indian Institute for Astrophysics.

Skyview

True to my religion, Physics, I thought an article on Astronomy and Astrophysics is a must! What you see above is how the sky looks like in a less than a degree field of view in a region of Large Magellanic Cloud, our next door galaxy. The image is taken by Ultraviolet Imaging Telescope.
Isn't it unbelievable that in that small part of the sky there are so many stars! And its so very beautiful. As if there is a Diwali in that galaxy, and all those are houses with diyas lit up on their doors.
And another amazing thing about sky-view is that, when you look in different directions, you are actually seeing light that originated in different times from those stars, so there is a temporal information encoded in the picture! What you see is a spatial collage of different pasts in various directions..

night sky of the World

night sky of the World

Above picture shows how much city light is emitted in different parts of the world at night... recorded by some satellites. More info is here:- night sky in the World. interesting, isn't it!

One hour day and Half hour night

I always feel grateful for being in a Research Institute. Its this sheer opportunity to meet some of the most brilliant people on the planet. Today we had a talk by the Astronaut Claude Nicollier, "My experience in Space".He showed some amazing pictures of the earth from space, it was simply fantastic to see the entire Himalayas in one picture. Also, the distribution of river Ganga where it meets the ocean.
It was also an absolutely stunning picture to see that on top of one of the desserts, the cloud coverage is exactly on top of the sea, and it ends on the coastline.

Absolutely passionate about his work, he mentioned how he had undergone rigorous training in water chambers. Their first mission was repair of the Hubble Space Telescope. Imagine changing parts of a huge (2 meter diameter) telescope in space! In those water chambers, they make exact replica, with high fidelity modelling, of the space telescope. In space you need to stabilize your body, and move very slowly. They practised it for months before the mission, in the water chambers. Exact and detailed planning, even practise of handling unexpected failures and problems.

When you are in space, you are in a very low air pressure surrounding. Say 1/3rd of that on earth. So the nitrogen tends to get into the blood. There are Air Chambers, where you increase the air pressure to normal ones on the earth, and rejuvenate yourself. Claustrophobia is the fear of enclosed spaces. If you have it, then these small Air chambers are not meant for you! Also the Astronaut's suit can be very cumbersome to get into and carry along.

You can see here a photo of a pair of astronauts repairing the Hubble Space Telescope. Notice that one astronaut has firmly grounded his feet on the robot arm of the space ship,(you don't see the spaceship, the arm is the white rod like thing in the photo), and other Astronaut is freely floating. Whenever the Astronauts are doing such work, doing space walk, they are attached to the space-craft by a thread: they are tethered. This is to ensure that they don't just get lost in space by mistake! As he jokingly said, if an astronaut or a repair tool is lost, it becomes a useless satellite to Earth! So all the repair tools and parts are also tethered to the spaceship.

As you are orbiting, you have sunrise and sunset more often! You get 1 hour of a day and 1/2 hour of a night! Of course, you don't go to sleep in that night when you are in shadow of the earth. So you need to get used to this kind of bright and dark timings. Before the Earth becomes totally dark, and Sun goes behind it, you can see a beautiful cresent of the Earth! The moon also rises and sets quite fast. The sky is absolutely dark, and you can see Sun also as just another, closer, brighter and bigger star.

On Earth, our body has mechanisms to push lot of blood supply to the head. So much supply is not needed when you are in space. Lot of body fluid imbalance and loss of orientation can happen when you just reach the space. So if you are planning to visit and go for a space ride, be prepared for some phisiological unpleasantness! He said its like sea-sickness.

To become an astronaut, he said, you need good physical fitness, sound mental balance, and a sound educational background. After that, its a luck to be selected, as there is lot of competition and few jobs available!

A Physics Graduate, who did research in Astronomy, and took over Air Pilot job, and then worked as an Astronaut, Claude Nicollier is now full time professor in Lausanne, inspiring young students to the thrill of Space research.

Q n A - 2 :- learning Physics during train travel!

I am happy when people recognize me as a Scientist, in particularly as a Physicist. In the train journey from Bangalore to Mumbai last night, I found many interesting youth in my compartment, asking lots of interesting physics questions. Here is roughly how the dialogue went on for almost two hours! Thanks to Alpa, Girish, Akhilesh, Keyur and Jitender for being such curious students!! And I like being grilled by questions, so thanks for grilling me!! :)

Q: What is the expected outcome of Large Hadron Collider? Can we create another planet from this experiment?
Ans:- Hardly! in LHC experiment,They are colliding two protons at a very high energy. Now, what do you think of a proton as? A kind of solid spherelike a cricket ball, but a tiny and very low mass one, right? In reality, even the proton is made up of smaller fundamental particles, called "Quarks".Now these quarks don't generally leave the spherical boundary of the sizeof the proton. However, when two protons collide on each other with so much energy, these quarks can break up into various combinations, and new particlescan get formed.
Q: So how does LHC experiement give rise to a new Big Bang?
Ans: It doesn't create a new big bang!! Its like this: When Big Bang Happened,Huge amount of Energy was packed in small region of space. And the laws ofPhysics as we know are not valid for such high energy densities. So we cannotstudy the physical situations very very close to Big Bang time. (We can, however,Go upto the microseconds after the bigbang!)So when two protons in LHC collidewith each other, what they do is they pack in a lot of energy in a very smallvolume, thus making a laboratory controlled situation similar in few aspects, to the big bang.
Q: So is it really worth spending all the money, on this biggest experimentof science? Cant we not use it for some social cause?
Ans:- I don't think that social causes are not being taken care, and lack onlymoney. Scientific advances have far reaching consequences not known beforehand.E.g. The GPS system which you use, would collapse in few minutes if the Einstein'sGeneral Theory of Relativity is not used in their calculations. Now GTR givesvery minute corrections, and most of the times we can use Newton's theory of gravitation. However, when your hand receiver gives out signal to 4 satellites,and they correlate their positions and send you back your location details, if they don't apply proper corrections for their positions, then your locationwon't be accurate at all! So who knows, results of LHC experiment may bring outsomething not forseen right now.
Q:So what is your research topic?
Ans:- I am studying the properties of interstellar dust, that between us and the stars. This dust obscures the starlight, and scatters and absorbs it, thusnot giving the correct picture. Its just like a cloud covering the sun. So if I know the size, constituents, spatial distribution of these dust particles,then I can account for their effects.
Q:- How is this dust?
Ans:- Its micron size. Anything more than a hundred atoms bound together is termed as dust. Q:- I thought space was all vaccum, how come so much dust, and how significant is the obscurration?
Ans:- YES, it is a very high quality vaccum out there. Its better than the bestthat can be achieved in laboratories... Still, inside the galaxy, there is lot of hydrogen gas, and also these dust particles.And there is hardly one particleper cm^3, but the distances are so Huge, that it adds up to a large quantity.
Q:- What is this dust made up of?
Ans:- Its largely silicates, oxides, carbon and ice.Q:-If we see a spectra of dust, what do we exactly see, the dust, or the sourceof the light?Ans:- The scattered light will be of the same frequency as the source. The dust absorbs some light, and gets heated up, and emits in Infrared, just likeeven now all our bodies are radiating in Infrared. Now some of the absorbed lightwill excite the atoms in the dust to a higher level, and when it de-excites, it will emit the spectra charecteristic to the dust constituents.
Q:I just don't understand all this, Big Bang and stuff like that. What was therebefore that?
Ans:- Yeah. This is a limitation of linear logic. You will always ask, what was before whatever you know, and what is after whatever you know! Another scheme of logic is spherical logic. Its like this, on a sphere, what is the starting point of the sphere? Any point could be a starting point. This is a gift of Indian Philosophy to the Scientific thinking. There is also a theoryfor beginning of universe, that there was not just one big bang, but millionsand millions of big bangs. Right now there could be something like a Big Banghappening in a distant part of the world!Alpa:- Right now there could be other copies of us sitting in some other part of the world! Me:- Yes very much possible!
See this article.
Q:What is dark matter? how come it became known recently?
Ans:- Its non-barionic matter, matter which doesn't give out electromagneticradiation. Protons are barionic matter. Recently, Astrnomers studied the velocityof hydrogen in different parts of the galaxy, and plotted it from the center of galaxy radially outwards. The velocity curve flattened after a radius, and thiswas not acceptable, gravitationally, if you assume that only the luminous matter is present.So they had to suggest a large amount of unseen matter, which theytermed as dark matter. In absence of any such matter, the curve would have gonedown, instead of remaining flat.
Q: What if I emit light from a car travelling at the speed of light!? Will I see it in front of my car?Ans:- First let's consider a simple situation. Lets say I am standing here, and you are travelling in a car at speed V1. And you throw a ball at speed V2 in same direction. Then I would notice the speed of that ball as V1+v2, right? Now consider the case of light. If you are travelling at speed v, and throw light, which will travel at the speed c, then I will also see the light travelling at speed c!! This is a kind of miracle! This is an experimentally verified fact,and This is subject of relativity, where our notions of time and space are totally changed! E.g. If Akhilesh travels from here to a distant galaxy and comes back, he would find himself younger than his cousin, whom he left at the same age!! This is because, not just clocks, the heartbeats, the wheels, the time itself slows down for a moving observer, w.r.t. a stationary observer!!Girish:- There is a nice description of this in Concepts of modern physics byArthur Beiser.Me:- Yes, and Relativity is not difficult! With pen and paper I can describe to you in few minutes!
See this nice illustration.